Field-devices/measuring devices e.g. for measuring and/or monitoring the fill level of a medium in a container are produced and sold by the assignee. These measuring devices deliver their measured values, or, in general, the chemical or physical process variables, usually on a field bus for further processing. Desirably, the measurement data are as current as possible, so that they reflect the current state of the medium. This is, above all, relevant, when the frequency of the fetches or queries lies in the order of magnitude of the possible measuring frequency. Consequently, the measured data should be produced just shortly before the communication. For this, however, it must be known, when the query will occur through the field bus. This point in time depends e.g. on how many measuring devices are connected to the field bus. If the number of measuring devices is increased, then the time spacing between the queries becomes greater. Also, the configuration of the whole system can be changed, so that the spacings vary. Thus, there are no rigidly predetermined time spacings. This problem arises especially, when the query comes over the field bus from a central control unit and when the field devices do not communicate their data independently or at least do not know about the remaining happenings on and around the field bus. If the queries occur in sufficiently large time spacings that, in the meantime, plural measurements are possible, then it can be desirable to reduce energy consumption by avoiding the taking of measurements which will not be fetched anyway.